Human leptospirosis, an anthropozoonoses,  in India is still being underreported though it has gained extreme public health importance, because of huge livestock and rodent populations and poor sanitary conditions. From 2008 to 2012, about 1730 serum samples from  human cases with pyrexia of unknown origin (PUO) from various hospitals in Namakkal district of Tamil Nadu, India  were screened by dark ground microscopy (DGM). A positivity of 51.7 % was observed and 85 % of the positive cases manifested a milder anicteric leptospirosis. High positivity was observed in truck drivers (65.8%), age group of <20 years (55.4%), males (54.0%) and north-east monsoon (53.2%), and from the calculated relative risk (RR), a strong positive association could be observed for truck drivers and males with the occurrence of leptospirosis. A prompt epidemiological investigation in susceptible animal population along with an unequivocal diagnosis of positives in humans exposed to the risk factors, in association with the periodical vaccination of susceptible animals and control of rodents, could possibly halt the emergence of the disease.